May in West Allis averages a daily high of 20.7°C with nights around 8.7°C. Expect roughly 13.6 wet days totalling 113.7mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit West Allis is August–September.
Based on WEST ALLIS, WI US (2.5km), 1995–2024. 14 years of May data.